Propulsion unit



Nov. 19, 1963 J. c. TRoTTl-:R

PROPULSION UNIT '7 Sheets-Sheet 1 Filed May 3, 1962 JOHN GJFOTTE/i BY @M M. M4911,

ATTURNEYS Nov. 19, 1963 J. c. TRoTTl-:R

PROPULSION UNIT 7 Sheets-Sheet 2 Filed May 3, 1962 f/ 1NVENTOR JoH/v c. #POTTER @.M, Il

ATTo/VEYS Nov. 19, 1963 J. c. TROTTER PRoPuLsIoN UNIT 7 Sheets-Sheet 5 Filed May 3, 1962 INVENTOR. JOHN 0. TROEH ATTORNEYS Nov. 19, 1963 J. c. TROTTER 3,111,103

PRoPuLsIoN UNIT Filed May 3, 1962 7 Sheets-Sheet 4 INVENTOR. JUHN G. THOTTEH @mwa ATTONEYS Nov. 19, 1963 J. c. TROTTER PRoPuLsIoN UNIT '7 Sheets-Sheet 5 Filed May 3, 1962 a INVENTOR /I BY" JOHN C. TROTTER @MQW/wm ATTORNEYS Nov. 19, 1963 J. c. TRoTTl-:R

PROPULSION UNIT 7 Sheets-Sheet 6 Filed May 3, 1962 INVENTOR.

JOHN C. TROTTER "Uwwaaeww ATTORNEYS Nov. 19, 1963 J. c. TROTTER PRoPuLsIoN UNIT 7 Sheets-Sheet '7 Filed May 5, 1962 ENG/NE BIG ENG/NE INVENTOR.

fNG/NE AT TOPN'EYS JOHN C. TROTTER United States Patent O lildtli PRUFULMN Ulsll' lohn C. rl'rotter, Williamsville, NY., assigner to Bell Aerospace Corporation, Wheatiield, NX. Filed May 3, 1962, Ser. No. 192,127 6 Claims. (Cl. 11S- 14) This invention relates to propulsion means for aquatic vehicles and in particular relates to such a propulsion means characterized by the provision of a plurality of propelling devices alternately usable so as to Ipositively assure the availability of an operative propelling device at all times.

Specifically, the present invention is directed to a mechanism adapted to positively assure the availability of propelling means for an aquatic vehicle and the invention therefore can be employed wherever such problem is of paramount importance. However, such requirement is particularly critical in relation to landing craft utilized for military purposes. in connection with such craft, it will be appreciated that the assurance of loperative propelling means at all times is of paramount importance and to this end, it is a primary objective of the present invention to provide such a mechanism as will assure that the craft will at all times have available a propulsion unit which is operative and ywhich will produce the requ-isite and theoretical power required lfor proper operation of the craft.

More particularly, the present invention has for its main objective the provision of a propulsion unit for military `landing craft in which at least a pair of propeiling means are employed, the two propelling means being alternately usable and operating as an integral unit, the structure characteristically providing for the operative disposition of one of the propelling means while positioning the other of the propelling means in such disposition and position as will permit ready access thereto by occupants of the craft so that repairs, cleaning and the like may be performed on the inoperative unit to ready it for instantaneous disposition into the operative position if circumstances so require.

Another object of this invention is to provide an improved propulsion unit of a character described fwherein in association with a common prime mover, a pair of propulsion units are provided, the two such units being connected for common rotation `about the mounting axis therefor so that one of the units is operatively disposed under water for propelling purposes, the other is elevated above the sur-face of the water and is presented in such position as to be readiiy accessible to occupants of the craft with which the assembly is associated so that the exposed unit may be cleaned, repaired or the like.

Further, it is an objective of the present invention to provide in association with the assembly as above described, cl-utch means automatically engageable when the operatively dis-posed unit is in position to connect such operatively ldisposed unit to the power supply while the other unit is disconnected from the power supply.

Another object of this invention in relation to a speciic embodiment thereof is to provide a dual propulsion unit as above `described wherein the propulsion units operate on the principle of expellingr a high velocity, high pressure stream or jet of water for propulsion purposes, the two units being provided with screened or `'grated intakes so positioned and disposed that when a unit is placed in the inoperative position, such screen will be readily accessible to an occupant of the craft for cleaning purposes, the grate or screen also being movably mounted on the -body of the propulsion unit so as to admit of ready access to the interior thereof.

Other objects and advantages of the invention will rice appear from the description hereinbelow and the accompanying drawings wherein:

FIG. l is a vertical section taken through one form of the present invention showing various details of internal construction thereof;

FIG. 2` is a rear elevational view of the assembly shown in FIG. 1;

FlG. 3 is an enlarged vertical section taken substantially along the plane of section line 3-3 in FIG. 2 illustrating details of the drive `and clutch mechanism to show one yform which the same may take;

FiG. 4 is a horizontal section taken substantially along the plane of section line 4 4@ in FIG. 3 showing further details of the clutch mechanism;

FlG. 5 is a vertical section taken substantially along the plane of section line 5 5 in FIG. 3 showing still further details of the clutch mechanism;

FIG. 6 is a horizontal section taken substantial-ly along the plane of section line 6-6 in FIG. 3 showing details of the control mechanism for the propulsion assembly;

FIG. 7 is a side elevational :View partly in section illustrating a modified form of the invention;

FIG. 8 is a rear elevational view of the assembly shown in FIG. 7;

FIG. 9 is a view similar to FlGS. 1 and 7 but showing a still further modified form of the invention;

FIG. 10 is a diagrammatic view showing the relationship of parts in association with forms of the invention as lare shown in FIGS. l and 7;

FIG. l1 is a View similar to FIG. 10i' but showing the association of parts in the form of the invention shown in FG. 9; and

PEG. l2 is a view similar to FIGS. l0 and l1 but showing a further modification of the present invention.

Referring now more particularly to FIG. l, the reference numeral indicates in general a transom of an aquatic vehicle which in the specific embodiment shown serves as the main supporting port-ion of the craft to which the present invention is attached. The aquatic vehicle yor the like is shown mainly in phantom lines in FIG. l since it forms no part of the present invention. However, the aquatic vehicle carries some sort of prime rnover mechanism indicated generally by the reference character 712i which sup-plies power for the propulsion assembly indicated generally by the reference character 14. For this purpose, the drive shaft lo -is provided which extends from the prime mover 1.2; for connection, as hereinafter more particularly pointed out, to the assembly 14 for driving the same.

For mounting purposes, -a rigid sleeve l is provided, the same having a suitable iiange or the like 2G thereon which is secured directly to the transom itl* by means of suitable fasteners such as those indicated by reference character 22. r.ihe sleeve liti` mounts a hollow shaft member 24 by means of suitable bearings Z6 and the drive shaft i6 projects concentrically through the hollow shaft 24, substantially as is shown.

The hollow shaft extension 24 which is journaled in the sleeve lil is rigidly formed with a hollow head memer 28 which is provided at its opposite ends which project laterally from the shaft extension 24 with propulsion units indicated generally by reference characters 3o and 32. The two propulsion units 3o and 32 are provided with attachment flange portions 34 and 36 which are interconnected by means of a semicircular connector plate 38, the same being provided with flange portions do and 42 corresponding and engaging with the flange portions 34 and 36 and fixedly secured thereto by any suitable fastener means as may be desired. Thus, the two propulsion units El@ and 32 are rigidly interconnected by the plate member 33 and are therefore independently movable relative to the crosshead 2S. For this purpose, the units 3@ and 32 may be journaled on the crosshead 23 in a suitable fashion, not shown, by means of which the propulsion units El) and 32 are rotatable about the axes of pump shafts 44 and 46 journaled within the crosshead 2S, as hereinafter described.

Each of the propulsion units 36 and 32 is of similar `configuration and each includes an outer housing portion 48 provided with an intake opening normally covered by the intake grate or screen assembly 511 in each case. Preferably, the intake screen is hingedly mounted as at 52 to the body 48 and suitable latch means such as the mechanism 54 is provided to normally retain the grate or screen assembly in place relative to the body 42S. lnternally of the housing or body 143, there -is provided a pump shroud 56 housing an impeller assembly indicated generally by reference character 58. The impeller assembly 58 is attached to one of 'the corresponding shafts d4 or 46 and operates within the shroud 56 to draw water through the openings 6i) and 62 therein, as is shown by the arrows in FIG. 1 to ultimately discharge such water through the discharge end 64 of the assembly. The jet or stream of Iwater issuing from the opening 64 provides the propulsive effect for the associated aquatic vehicle.

The details of the pumps in each case form no part of the present invention but suffice it to say that each is provided with a reversing hood assembly indicated generally by reference characters 68 and 71B by means of which the craft may be operated in forward as well as reverse directions. These two hoods are interconnected for common actuation by means of a bell crank 72 pivotally mounted as by a shaft 74 carried by the interconnecting plate assembly 33, there being two tie rod assemblies 76 and 78 extending from this bell crank to the respective hood devices 68 and "70". The opposite end of the bell crank is connected, as at 82, to a suitable control member such as the control wire 'S4 so that the bell crank may be swung between the full and dotted line positions as shown in FIG. l whereby the two revers-ing hoods 61S and 70 are likewise swung between the full and dotted line positions as is shown. The control wire 34 may work on the Bowden wire principle, the outer sheath S6 therefor being anchored as at 88 Ito the interconnecting plate 38 and the entire assembly extending therefrom to within the confines of the aquatic vehicle for remote operation of` the reversing hood mechanism as will be readily appreciated.

As is shown in FIG. 3, the crosshead 28 comprises simply an elongate tube member extending at right angles to the hollow shaft extension 24, such member 2S being provided internally with suitable internal anges 8i) and S1 receiving suitable bearings 83 and 85 which journal and mount pinions 88 and 90, both of which are in mesh with a common pinion gear 92 aixed to or formed integrally with 4the inner end of the drive shaft 16. Bach of the pinions '8S and 90 is provided with a spline shank mounting respective clutch elements 94 and 96 thereon which clutch elements are rigidly aflixed to their respective pinions. Mating clutch elements 98 and 1613 are splined or otherwise suitably aiixed for sliding movement on the inner ends of the impeller shafts d4 and 46, substantially as is shown. By mechanism subsequently -to be described, the propulsion unit which is in operative position is coupled to its associated pinion 88 or 90 whereas the inoperative propulsion units are disconnected from their corresponding pinion or pinions. Thus, in FIG. 3, the impeller shaft 46 is shown ywith the two clutch elements 96 and 100 drivingly interconnected or coupled together. In the specific form of the invention shown in this ligure, the clutch assembly is ofthe dog clutch or dental type.

The manner of operation of the clutch assemblies will be seen more clearly from a study of FIG. 5. In this figure, it will be appreciated that the housing or crosshead 28 mounts a pair of dog cranks 1112 and 104 about respective pivot pins 106 and 108i. Each of the clutch elements 9S and 100 as is shown specifically for the clutch element 93 in FlG. 5 is provided with a collar 11d on its shank 112 spaced from the dental clutch element proper so as to provide a circumferential groove there between within which rides the beaded end 114 of the crank arm 116. The other end 118 of each crank is provided with a roller element 12@ mounted upon a pivot pin 122 and which rides against the cam 124 rigid with or otherwise iixedly secured to the housing member 18. This cam surface is provided with a lobe 126 which is so oriented with respect to the two bell crank rollers 12d and 128 as to cam the lowermost disposed bell crank, in the case of FlG. 5 the be'll crank 1M., so as to interengage the corresponding dental clutch elements 94, 98 or 96, 160. Tension springs 13h and 132 are associated with the two bell cranks 1.62 and 16d substantially as is shown so as to maintain the rollers 129` and 128 in engagement with the cam 12d, such springs acting to automatically disengage 4the associated clutch assemblies whenever the rollers or 128 have passed beyond engagement with the cam lobe 126. Thus, there is provided a positive clutching action and a resilient declutching action.

The crank arms 116 and `11b are offset from each other as will be seen from FIGS. 5 and 6, the crank arm 116 in each case being internally disposed relative to the housing 218 and preferably being in the form of a bifurcated form having spaced arm portions 146 and 142 substantially as is shown -in FIG. 6 and the external crank arm 11S being rigidly connected at its hub 144 to the outer end of the pivot shaft 106. The pivot shaft 166 is each caseV extends through and is journalled in a suitable hub portion 146 formed integrally with or otherwise rigid with respect to the housing 2S, substantially as is shown in FIG. 6.

FIG. 6 also illustrates a portion of the steering control for this particular embodiment of the invention. As shown, the interconnecting plate 3S is pro-vided with a lug 151i cooperative with a bifurcated steering arm 1512 whose spaced leg portions I1-54 and 156 straddle such lug and are pivotally secured thereto as by a pivot pin i158 so that the steering arm 152 may pivot up and down in a vertical direction. The steering arm 152 carries a ball at its free end captive within a suitable socket member 161! having connection at opposite sides thereto to steering cables 162 and 164, which pass therefrom around suitable corresponding pulleys `166 and i168 and the cables thence pass forwardly of the craft to suitable steering control mechanism as will be readily apparent. The purpose for the pivot pin 158 is to prevent binding in the steering mechanism should the propulsion assembly be rotated about the axis of the housing i118 when the steering mechanism is in other than a straight ahead position, under which circumstances vertical pivoting action of the steering arm 152 would be necessary to accommodate for such rotation of the propulsion assembly. This relationship will be more cleanly evident from a study of lFIG. 2 which, in the position as is shown, represents a straight ahead position of the propulsion assembly, the propulsion assembly being shown in dotted lines in the process of being switched end for end or pivoted about the axis of the housing 23.

`FIG. 2 taken in conjunction with lFIG. 1 illustrates the manner in which the pivoting of the propulsion assembly may be achieved. In this specific instance, an extension of the member 24 has a collar 170 rigidly affixed thereto and projecting laterally, normally horizontally, from this collar 1'70 is a bar member 172. Thus, when it is desired to reverse the propulsion assembly .114, the bar r17 2 is simply moved from the full line position shown in fFIG. 2 to an opposite full line position wherein it will be displaced 18(11 from that position shown in FIG. 2. An intermediate position of such bar 172 is shown in dot-ted lines in FIG. 2 and the corresponding position of the propulsion assembly .14 is also shown in dotted lines in such figure.

Referring now more particularly to FIGS. 7 and 8, a modication is illustrated therein, although the same does not depart from the basic concepts of the invention thus far described. In FIGS. 7 and 8, the rigid mounting sleeve is indicated by reference character 180, the same being provided ywith a suitable collar y182 for fixed securement to the craft with which the propulsion unit is associated, such fastening being obtained for example by fasteners 184 as shown. The crosshead 186 which rigidly mounts the two propulsion units e183 and 190 at its opposite ends is provided with a tubular extension 192 projecting lwithin the mounting sleeve 180 and suitably journalled therein as by bearings `194 and 196. It will be appreciated that since the two propulsion units 188 and `19) are rigidly afiixed to the crosshead i186, such propulsion units are not movable for steering purposes. Instead, suitable rudders or vanes 1918 are provided in association therewith to effect the proper directing of the jet or stream of fluid issuing from the propulsion units 138 and 19t). Steering connection to these rudders 19-8 is made by means of a pitman arm 290 having a horizontal aligning pivot 262 connecting such arm 2li!) to the crank 264. T he crank 294 is pivoted by means of a vertical pivot member 206 to an aft projecting bracket 203 rigid with the crosshead assembly i186, substantially as is shown. The crank 204 is pivotally connected as at 210 to a link member 21'2 having connection with an arm rigid with the shaft member 214 which, through the medium of a further arm and link member 216 connects to the steering arm member 218 suitably connected to the rudders 123 to effect turning thereof in response to movement of the pitman arm Zlll). The pitman arm is connected at its 'aft end to a steering cable 220 which runs within a fixed tube member 222 connected as by brackets 204 and 2G6, see particularly IFtlG. 8, to certain portions of the craft and this tube is slotted as is shown in FIG. 7 to receive the aft end of the pitman arm 200 and the cable 220 is connected to suitable steering means to effect rudder control as aforesaid.

The propulsion units 1818 and '190i are also provided with reversing hood assemblies 224 and 226, each of which is provided -with rigid extension arms 230' and 232, see particularly FIG. 8. These arms 230 and 232 are pivotally connected to links 234 and 236 in each case ywhich are journallled at their opposite ends on the interconnecting bar 2318. The bar 238 is pivotally connected to the aft end of an arm 24o of a bell crank mechanism pivotally mounted as at 242 -to a fixed ear 244 on the crosshead 186. The other arm 246 of this bell crank is pivotally connected .to the aft end of a drag link 248 which extends therefrom to a point of pivotal connection as at 25d to the outer ring member 252 of a swash plate assembly indicated generally by the reference character 254. The inner ring member 256 of the swash plate assembly 254 is pivotally mounted about an axis indicated by reference character 258 to the mounting sleeve 181i and suitable connection (not shown) is made -to this inner ring 256 for pilot control to tilt the ring about the horizontal axis 25S to effect the corresponding movement of the reversing hood assemblies.

To effect selec-tive disposition of the units 188 or 190 in operative position, lock mechanism 26o is released so as to free the annular member 262 `which is rigidly connected to the two units 188 and E190 substantially as is shown. The lock mechanism may be provided with a manual release handle 2164 and also remote release mechanism including the bell crank 266 and rassociated cable control 268 extending to the pilots station.

Referring to FIG. 9, a lfurther modification of the present invention is shown therein. in this case, a mounting sleeve 27@ is once again utilized for direct connection to the associated hull and the crosshead yassembly 272 is likewise rotatably mounted within the mounting `sleeve 27 (l. As in the modification shown in FIGS. 7 and 8, the propulsion units 274 and 276 are rigidly affixed to the crosshead 272 and suitable rudder assemblies 278 `are utilized instead. These two propulsion units are also provided with suitable reversing hood 4assemblies 28o and 282, the construction being in general 'the same as is shown in FIGS. 7 and 8. rllhe construction 'of the individual propulsion units 274 and 276 is somewhat different from the forms previously described. In the instance shown in FIG. 9, each propulsion unit includes an irnpeller member 2E@ cooperating with fixed vanes 286 and a diffuser 28d, substantially as is shown whereby the fluid is inducted and discharged as indicated by the arrows in FIG. 9. The inipeller in each case is fixed relative t0 an elongate drive shaft 2% which extends substantially parallel to the center line of the `associated lhull and projects forwardly from its associated unit to terminate in a clutch element 222 as is shown. The drive shaft 2% of the prime mover is provided with Aa slidable clutch element 2% and a throwout fork 2% and associated control failli are provided for selectively coupling the prime mover drive shaft 29H4 with the selected one of the propulsion units.

Thus, it will `be evident that the construction sho-wn in FIG. 9 is similar to the `diagram-matic illustration of FIG. ll. That iS, a prime mover 392 is selectively coupled to the drive shafts 30d and Sli-5 of the two propulsion units ii and 31? by means of the common clutch indicated general-ly by the reference character 312, the two propul- Sion units `being pivotally rotated about a suitable mounting member axis at 3M. FIG. l0 illustrates the coupling connection `for the form of the invention shown in FEC-S. 1-8. In thi-s figure, the prime mover is indicated by reference character 336 and its drive shaft by reference character S Awhich simultaneously drives the output stub shafts which are connected to the pinions 32@ and 322. The operatively positioned propulsion unit 32d is coupled by clutch lassembly 326 to its associated stub output shaft While the clutch assembly 328 is disengaged.

FIG. l2 illustrates a further modification of the system which although similar to trat shown in FIG. l0, dir'cr therefrom in that the propulsion units indicated lby reference characters 33t? and 332 are of -a different type than thus far disclosed. This particular type of propulsion unit in each case constitutes a ducted fan, having a blade 334 and shrouding 336 surrounding the same. This type of propulsion unit is particularly 'well `suited for low speed operation since it has a high mass rate of flow at relaatively low velocities.

In any case, it will be appreciated that the propulsion assembly Idisclosed herein is directed to a mechanism wherein -a plurality of propulsion units are provided, the same being disposed in circumferentially spaced relationship with respect to each other, the several units being pivotally mounted `about a comimon center so that a selective one of the propulsion units may be disposed in operative position for driving the associated aquatic vehicle. The disposition of at least one of the inoperatively disposed propulsion units is such 'as to permit ready access to the intake :grate or screen thereof so that the same may vbe cleaned to permit the unit to subsequently work at maximum capacity. Preferably, such grate is 'also so associated `with the Imoving parts of the propulsion unit that access thereto may be easily had. lt will be obvious that although only two propulsion units are shown in each propulsion assembly, any `desired number of individual propulsion units maybe provided.

l claim:

l. In an aquatic vehicle having la hull,

la propulsion `assembly including a frame pivotally mounted on said hull about a generally horizontal axis for positionally fixed adjustments thereahout, plurality of individual propulsion units carrie-d by said frame in radially offset relation to the pivot axis for said frame and disposed in circumferentially spaced relation to each other about such pivot axis for the frame, said pivot 'axis lbeing located on said hull above the waterline thereof a distance less than the radial offset 7 of said propulsion units so that at least one of said propulsion units is disposed above water while at least one other is disposed in operative, itl-water position,

4. In an aquatic vehicle having a hull,

a propulsion assembly including -a Eframe having a generally horizontal tubular extension projecting from said hull,

power plant lin'eans mounted in said hull, 5 hull-carried shearing means engaging said extension and means for selectively connecting that propulsion whereby the propulsion un-it is positionally adjustunit which is in operative position to said power able relative to sai-d hull, plant means. a pair of propulsion un-its on said frame disposed in 2. In `an aquatic vehicle having a hull, radially spaced relation to the axis of said tubular a propulsion assembly including a frame pivotally 10 extension and circumferentially spaced with respect mounted on said hull, to each other, a plurality of individual propulsion units carried by a power plant Imeans mounted in said hull,

said frame in radially offset relation to the pivot drive means connected to said power plant means `and laxis for said frame and in circumferentially spaced projecting from said hull, relation relative to the pivot axis of said trarne, and coupling means for selectively connecting said prosaid pivot Iaxis being located on said hull above the pulsion units to said drive means,

-waterline thereof a distance less than the radial oiiset said coupling means Ibein-g responsive to the position of said propulsion units so that at least one of said of said propulsion units so that the uppermost of such propulsion units is disposed above water while at units is idle for cleaning and like purposes while the least one other is disposed in operative, in-water 2() lowerrnost of said units is connected to Isia-id Idrive position, .means. rneans for lixing said frame relative to said hull such 5. In the vehicle as delined in claim 4 wherein said that any selected one of the units is disposed in operadrive means is a shaft extending through said tubular tive, vehicle-propelling position -whiie another of the extension and said :coupling means is a pair `of clutches units is disposed above water `so las to be exposed to interposed between said shaft and the individual propulhull-carried personnel `for cleaning and the like. sion units. 3. lnian aquatic vehicle having ahull, 6. ln the vehicle as defined `in claim 4 wherein said a propulsion assembly including ya frame having ya gendrive means is a drive shaft projecting from said hull erally horizontal tubular extension, below said tubular extension, hull-carried bearing means engaging said extension each propulsion unit having a driven shaft projecting whereby the propulsion lunit is positionally adjusttherefrom toward said hull, -able relative to said hull, each `driven shaft having a clutch element thereon yand a pair of propulsion units yon said frame disposed in said drive element having `a clutch elernent thereon, radially spaced relation to theV axis of said tubular such clutch elements forming said coupling means. extension `and diametrically opposed to each other, a power Plant 'mounted in Said hun, Refelences in the le 0f this patent a drive shaft connected to said power plant and pro- UNITED STATES PATENTS jectlng throu-gh said tubular extension, said drive shaft being connected to both of said pro 737,386 Gibbons Aug. 25, 1903 pulsion units, 40 3,027,862 Votre Apr. 3, 1962 `a Iclutch associated -with each propulsion unit, 3,030,909 Barnes et al Apr. 24, 1962 and means for maintaining the clutch of one propul- 3,041,831 Sin-gelrnann July 3, 1962 sion 1unit engaged while the clutch of the other propulsion unit is disengaged, FOREIGN PATENTS said means being responsive to the position of said 874,147 France Apr 2() 1942 propulsion units so that the uppermost of such units 1)()4465 5 Germany NOV. 20J 1958 is idle for cleaning and like purposes. 

1. IN AN AQUATIC VEHICLE HAVING A HULL, A PROPULSION ASSEMBLY INCLUDING A FRAME PIVOTALLY MOUNTED ON SAID HULL ABOUT A GENERALLY HORIZONTAL AXIS FOR POSITIONALLY FIXED ADJUSTMENTS THEREABOUT, A PLURALITY OF INDIVIDUAL PROPULSION UNITS CARRIED BY SAID FRAME IN RADIALLY OFFSET RELATION TO THE PIVOT AXIS FOR SAID FRAME AND DISPOSED IN CIRCUMFERENTIALLY SPACED RELATION TO EACH OTHER ABOUT SUCH PIVOT AXIS FOR THE FRAME, SAID PIVOT AXIS BEING LOCATED ON SAID HULL ABOVE THE WATERLINE THEREOF A DISTANCE LESS THAN THE RADIAL OFFSET OF SAID PROPULSION UNITS SO THAT AT LEAST ONE OF SAID PROPULSION UNITS IS DISPOSED ABOVE WATER WHILE AT LEAST ONE OTHER IS DISPOSED IN OPERATIVE, IN-WATER POSITION, POWER PLANT MEANS MOUNTED IN SAID HULL, AND MEANS FOR SELECTIVELY CONNECTING THAT PROPULSION UNIT WHICH IS IN OPERATIVE POSITION TO SAID POWER PLANT MEANS. 